Preparation of a spheroidal fischer-tropsch catalyst



N0V M, 1950 R. N. WATTS PREPARATION OF A SPHEROIDAL FISCHER-TROPSCH CATALYST Filed Sept. 30, 1948 GLJN P 0 L n e v n 5 WATER. IN I.ET

Patented Nov. 14, 1950 PREPARA'IION OF A SPHEROIDAL FISCHER-TROPSCH CATALYST Rhea N. Watts, Baton Rouge, La., assignor to Standard Oil Development Company, a corpo ration of Delaware Application September 30, 1948, Serial No. 51,987

The present invention is concemed with an improved process for the preparation of catalysts comprising iron microspheres. The invention is more specifically concemed with an improved iron catalyst adapted for promoting the synthesis of hydrocarbons containing more than one carbon atom in the molecule from feed gases comprising carbon monoxide and hydrogen.

Inan abandoned copending application Ser. No. 738,915 fiied April 2, 1947 entitled Hydrocarbon Synthesis Catalyst of which the present application is a continuation-in-part there is described a method for preparing iron microspheres from iron wire empioying a metallizing gun.

It is well known in the art to conduct hydrocarbon synthesis reactions by contacting hydrogen and oxides of carbon with catalysts under various temperature and pressure conditions.

The catalyst employed is usually seiected from the iron group metals, as for halt and nickel.

The temperatures employed in the synthesis reaction vary widely, as for example, in the range from about 300 F. to about 800 F. and are generally in the range from about 350 F. to about 750 F. The pressures, likewise vary considerably and are a function of other operating conditions, such as catalyst employed, activity of the catalyst, character of the feed gases and the temperature utilized. Pressures in the range from about 1 to 100 and higher atmospheres have been suggested. Satisfactory pressures are in the range from about 50 pounds to 750 pounds per square inch. The character of the feed gases introduced into the synthesis reaction zone depends somewhat on the particular temperatures and pressures, and upon the catalyst employed. For example, when empioying cobalt type catalyst, it is preferred to use about 1 mol of carbon monoxide to about 2 mols of hydrogen, whi1e when an iron catalyst is utilized, the mol ratio of hydrogen to carbon monoxde in the range from about 1/1 to 4/1 is desirable.

The synthesis gases comprising hydrogen and carbon monoxide areproduced by various procedures. Methaneor natural gas may be con- Verted to C and H2 in the presence of a reducible metal oxide, with pure oxygen or by reforming with gases such.as steam, CO2, or a mixture thereoi'. Other sources of C0 and H2 are coal, shale and other solid hydrocarbons which may be treated with steam at elevated temperatures. The reaction may be conducted in a single or in a plurality of stages. For example. one procedure is to reform metharie using steam, methane example, iron, co-

Claims. (Cl. 252-443) and carbon dioxic'ie and a nickel catalyst for the production of carbon monoxide and hydrogen. When employing methane as feed gas and oxidizing the same with a reducible metal oxide, the reactions are generally conducted at temperatures in the range from about 1400 F. to about 2000 F. When the synthesis gases are produced, by utilizing oxygen and natural gas, the temperatures in the synthesis gas producing zone are usually in the range from about 2000 F. to about 3000 F.

It has, heretofore, been known in the art to contact gases and solids by passing the gases upw.rdly through an enlarged treating zone, containing a body of finely divided solids to be contacted, at a controilecl gas velocity to maintain the solids in the treating zone in quasi-liquid or fluidized state. Under properly controlled conditions, the subdivided solid particles are not only maintained in a highly turbulent, quasi-liquid and ebullient state, but there exist a rapid and uniform circulation of the fluidized solids throughout the fluid bed.

Processes of this character, wherein fluidized solids are contacted with gases, have a number in inherent and important advantages. For example, intimate contact between the gases and the fluid subdivided solids is secured. -It is also possible to maintain a substantialiy uniform temperature throughout the bed as a result of the extremely rapid transfer of heat from one section of the bed to the other because of the rapid circulation of the fiuid subdivided solids. Furthermore, due to the rapld transfer of heat between the solids under these conditions, it is possible readily to add or extract heat from the mass at an extremeiy rapd rate. In these fluitiized reactions the small subdivided solids or catalysts usuaily have a particle size in the range from about 1 to 200 microns and higher. These particles are suspended in a fluid ebullient state by means of the upflowing suspending gases, the superflcial velocity (i. e. assuming no catalyst in reactor) of which varies in the general range from about 0.1 to 5 feet per second.

The inventon is primarily concemed with the production of catalysts comprising iron spheres. The iron spheres of the process are characteri2ed by having an iron core and an oxidized surface.

The cata1ysts are particularly desirable for employment in hydrocarbon synthesis processes in view of the fact that one problem and diiiculty in -synthesis operations is that the catalyst disntegrates due to the formation of excessive carbon on the catalyst. Apparently carbon forms throughout the area of the catalyst particies causing it to fragmentate. It has been discovered that, provided the catalyst particies comprise an iron core and an oxidized surface, the extent of the disintegration is restricted to the thick ness of the oxidized surface. As herenaifter described the extent and depth to which the surface skin is oxidized is limited by controlling the extent to which the molten iron particles are passed through air. The extent and depth to which the iron is oxidized on the surtace of the particles can be controlled by employing an atmosphere in which the oxygen concentration is controlled. For example, an atmosphere of nitrogen and oxygen can be adjusted so that a concentration below about 20% as tor exaxnple, in the range trom about 5 to oxygen may be tormed and the depth of the oxide illm on the iron spheres issuing from the gun thus controlled by passage through such an atmosphere On the other hand, it is within the concept of the invention to utilize an atmosphere in which the oxygen concentration is well above about as i'or example, in the range trom about to 60% and higher. A iew simple tests will determine the concentration of oxygen necessary to form an oxide iilm t desired thickness on the iron microspheres.

The catalyst particles of the invention are produced by using relatively pure iron wire as tor example iron wire which contains less than about 0.2% carbon and a metailizing gun. Any suitable metallizing gun may be employed.

Iron catalyst in order to be effective in hydrocarbon synthesis require a promoter. Usally an alkaii metal salt, oxide or hydroxide, in amounts of trom 1 to 5 weight per cent based on the iron. is utilized as the promoter or activator. In accordance with the present invention the catalyst in the form 01' small spheres is obtained by causing iron wire to pass through a device known as a metallizing gun and the prom0ter is inoorporated into or associated with, the iron particles thus formed, either by precoating the wire prior to passage through the said gun or passing an uncoated iron wire through the gun and quenching the molten particles issuing trom the gun in a solution containing the promoter whereby the iron spheres acquire the said activator in promotional amounts. In the accompanying drawing there is shown diagrammatically a metallizing gun.

Reerring in detail to the drawing, iron wire 2, either precoated with a suitable promoter as described hereinai'ter, or without promoter addition, is driven through metaliizing gun 4 by a. compressed air-operated turbine. The air may be diluted with an inert gas such as nitrogen to obtain the desired oxygen content in the compressed air. Oxygen and a suitable tuel, such as propane or acetylene, are admitted to the gun and admixed therein and are introduced through air cap 0. In the diagram, compressed air is shown passing through passage 0, iuel gas throush passage 10, and the wire ted throush I2.

The fuel mixture is ignited and burns at the end of wire nozzle l4 as indicated. The compressed air exhausted from the turbine blows against the melting wire to form an atornized spray of iron particles, which are allowed to impinge upon cooling water, the surace of which is at such distance trom nozzle I4 to allow the desired oxide coating to form on the atomi zed particles. One form of such quenching device is represented in the diagram. Cooling water with or without dissolved promotor is maintained in Approximately of the spheres were solid.

vessel |0 water being, i! desired, continuously admtted through inlet IB and withdrawn through outlet 20. At the bottom of [B there is preterably a receiver '22 for receiving the catalyst sprayed overhead trom metallizing gun l.

Using the particular metallizing gun described above, a reducing (with respect to the iron) atmosphere exists in front of the gun for approximately a distance of 6 inches. Thus when the metal is impinged upon a cold surace or quenched in a liquid within this dstance substantially no oxidized metal is deposited upon this surface. When the travel path 01' the metal particles is extended beyond the six inch limit, the extent to which the metal is oxidized is a function of the distance of its travel path beyond the reducing atmosphere. As pointed out heretotore, the operation may be conducted in an atmosphere in which the extent of the oxygen concentration is predetermined. The distance then becomes a iunction of the oxygen concentration of the atmosphere in which the operation is conducted.

The invention may be readily understood by the ioilowing examples illustrating embodiments 01. the same.

E:cample I gen pressure was 23 pounds per square inch and that of the acetylene, 15 pounds per square inch. The resulting spheres were colleeted, dried and screened through a 100 mesh sereen. The yield was 95% Analytical data on the spheres were:

Weight per cent Oxygen content by analysis 10 Total iron as Fe 90 Promoter as K2O (based on Fe) 0.4

The spheres consisted of approximately 74% FesOa. and 26 Fe.

Measurements of thes pheres and the oxide sur face coatings were:

'Ihieimoss Diameter 0! 0xide of Sphere Coating Mimms Mcimia 12 10 12 100 20 20 10 1.30 15 spheres of.the order of 40 microns in diameter had coatings about 15 microns in thickness. Spheres 20 microns in diameter were wholly oxidized.

A Roller analysis of the spheres was as tollows:

Mierons Per cent The remainder were hollow or irregular.

Ex ample II Microspheres were prepared by spraying iron wireeoatedwithKzainthetormotapaste i'rom a metallizing gun into water trom a distance of 20 inches. The amount of K:CO: used was such as to incorporate about 0.5% potassium as K. O on the i'ormed spheres.

Ezample II! The catalyst prepared according to Example I was tested in a, iiuidized hydrocarbon synthesis run to determine its activity and resistance to i'ragmentation, with the results below.

Temp. in reaction zone, 650 F.

Pres. in reaction zone, 400 lbs./sq. in. gauge Gas feed rate (vols. of total feed per vol. of

charged catalyst per hr.) 1515 SCF H2 to 00 ratio in total feed, 2.1 te 1 00 conversiou, 98.4%

CO+H: conversion, 98.3%

Yield, cc. of (24+ material per cu. meter of (H2+CO) converted, 199

At the end of the test (131 hours) it was noted that the catalyst iron core had not undergone tragmentation although the spheres had to a certain extent. swelied and/or agglomerated. The swelling occurred in the oxide coating however, and the swolien coatings underwent some disintegration but there was nu disintegration of the solid iron cores. During the swelling of the coating the solid iron cores became activated on their surfaces resulting in solid catalytic spheres which were not subject to disintegration but which did exhibit normal activity and selectivity even when substantiaily all of the coatings had been removed mechanicaliy.

E'xample IV The microspheres were promoted with K2CO: by adding 17.3 g. of K2COs.I H20 dissolved in 20 m1. 01 hot water to 438.5 g. of spheres. The catalyst was dried and utiiized in a hydrocarbon synthesis operation with the following resu1ts:

Iron Micros'pheres (Fixed Bed) (Oxidized 74%) 2.5% K100:

A B 0 D Yiel co ected:

'Oil, cc/m' H+CO consumed- Cc. hydrocarbon of butane and higber bolling constitunts.

Example V tance before allowing it to hit the water. On a weight basis the microspheres were about 60% 1"83Q4. Examination of mounted microspheres metaliographically revealed solid ironcores with iron oxide coatings varying trom 3 to microns. An analysis of the spheres was as follows:

Microns Per cent These spheres were employed in a hydrocarbon synthesis process with the i'ollowing resuits.

Iran Micrcspheres (ma:

Surfsce +2.0% K:C

Operation A B 0 Tom ture. 600 600 Feed lIz/CO Ratio 0.02 0.92 0.92 Ylelc1s, collected:

011, ce/ln' HrI-CO consumed--- 114 114 E'zample VI The cataly st prepared as described in lhia mple V was empioyed in fluid bed operations. '1'he results were as foilows:

Operation A B 0 'lempemture F 650 650 650 Pressurn L 400 400 400 2/1 2/1 2/1 Prop ane, plus 221 240 243 Butane, plus 193 203 zo:

' Cc. of propane.

butane and higher boiling constituents produced per m' of iron, spraying molten iron predominantiy in the form of substantially spherical particles substantially exclusively above 20 microns in diameter through an atmosphere comprising 5 to 60% oxygen and through a distance of trom about to about 3 feet and quenching the resultaat sprayed material in water, whereby solid iron spheres containing relatively pure iron cores and xidized coatings are obtained, controlling said oxygen percentage and said distance within the ranges indicated in such a manner that the thckness of said coatings is about 3-20 microns, and adding a promotional am0unt of a compound seiected from the group consisting of the oxides and carbonates of sodium and potassium by a method selected from the class consisting of pre-coating an iron wire, impregnating during quenching and impregnating after quenching.

2. The process of claim 1 in which said compound is potassium carbonate.

3. The process of claim 1 in which said catalyst microspheres comprise up to about 21% oxygen.

4. The process of claim 1 wherein said oxidizing atmosphere comprises air.

5. The process of claim 1 wherein said iron contains less than about 0.2% carbon.

6. A process for the preparation of an iron catalyst comprising iron microspheres containing iron cores and oxidized coatings, wherein said oxidized coatings may have thicknesses up to about 20 microns, which cmprises spraying substantially pure molten iron predominantly in the form of substantially spherical particles substantially exclusively above 20 microns in diameter through an atmosphere comprising 5 to 60% oxygen and throush a. distance oi. trom a.bout iio a.bout 3 reet and quenching the resultant spraaed meterial in water, whereby so1id iron spherea containing relatively pure iron oores and oxidized coatings are obtained, controlling said oxygen percentage and said distence within the rzmzes indicated in such a manner that the thicimess of said coatings is about 3-20 microns, s.nd adding about 2 to 4% by weight of K:CO: to said spheres.

7. The process of claim 1 Wherein said compound is incorporated into said spheres by dissolving said promotional compound in said water.

8. The process of claim 1 wherein sa.id compound is incorporated by precoating with said promoter said iron prior to melting.

9. The process of claim 8 wherein said K:CO: is dissolved in said water.

10. The process of claim 1 wherein sa.id iron is in the form of irou wire.

REEL N. WA'I'IS.

8 nmnmvcras crrnn UNI'IED STATES PA'I'EN'IS Number Name Date 446,988 Tilghman et al Feb. 24, 1891 1.695,041 Elmen Dec. 11, 1928 2,360,787 Murphree Oct. 17, 1944 23651120 Neighbors Dec. 28, 1944 2406864 Thomas Bept. 3, 1948 2417,164 Huber Mar. 11, 1947 2469,'755 Voorh1es May 10 1949 2,476,920 Sezura Juiy 19, 1949 2.480.341 Seelig Aug. 30, 1949 

1. A PROCESS FOR THE PREPARATION OF AN IRON CATALYST COMPRISING IRON MICROSPHERES CONTAINING IRON CORES AND OXIDIZED COATINGS, WHEREIN SAID OXIDIZED COATINGS MAY HAVE THICKNESSES UP TO ABOUT 20 MICRONS, WHICH COMPRISES MELTING SUBSTANTILLY PURE IRON, SPRAYING MOLTEN IRON PREDOMINANTLY IN THE FORM OF SUBSTANTIALLY SPHERICAL PARTICLES SUBSTANTIALLY EXCLUSIVELY ABOVE 20 MICRONS IN DIAMETER THROUGH AN ATMOSPHERE COMPRISING 5 TO 60% OXYGEN AND THROUGH A DISTANCE OF FROM ABOUT 1/2 TO ABOUT 3 FEET AND QUENCHING THE RESULTANT SPRAYED MATERIAL IN WATER, WHEREBY SOLID IRON SPHERES CONTAINING RELATIVELY PURE IRON CORES AND OXIDIZED COATINGS ARE OBTAINED, CONTROLLING SAID OXYGEN PERCENTAGE AND SAID DISTANCE WITHIN THE RANGES INDICATED IN SUCH A MANNER THAT THE THICKNESS OF 